The preservation of cut flowers by means of chemical treatment, which may or may not include a dyeing step, is well known and has been practiced for a long time, as for example, described in PCT International Publication No. WO91/03160 (U.S. Pat. No. 5,252,537), U.S. Pat. No. 6,365,548 and others. However, all of the taught methodologies offer several challenges when attempting to operate on a commercial scale where large quantities of material are required to be treated and where a consistent quality end product is desired. Examples of such challenges include shriveling of flowers and leaves, inconsistent colouring during the dyeing process, inconsistent uptake of preservative (too wet or too dry material), etc.
In the treatment methods disclosed in the prior art, some of the water in the cellular structures of the plant material is removed and replaced with a chemical substance that acts as a humectant, examples of the chemical substance being glycerol and polyethylene glycol, amongst others. The humectant is usually absorbed into the plant material being treated by immersing the stems of freshly cut plant material into a diluted humectant solution in water and allowing the plant material to absorb the humectant by normal plant processes over several hours or days. For certain types of plant material such as firm flower heads, the preservation time may be reduced by submersing the entire plant material in the solution. Alternatively, some or all of the water in the solution may be replaced with a low boiling point solvent, for example ethanol, to increase the rate of evaporation from the leaves and thereby shorten the treatment time required. The excessive use of such solvents is, however, detrimental to cellulose. Such procedures are also difficult to control and often lead to poor quality, shrivelled products.
In addition to the humectant, the solution may contain a dye as required. When a dye is included in the treatment solution, the quality of the final products is often variable (inconsistent colouring and not “life-like”) and the colour often fades over time. To overcome some of these shortcomings, plant material may be subjected to one or more bleaching protocols prior to preservation and/or dyeing. Bleaching protocols may, for example, include one or more bleaching steps using oxidative bleaches such as hypochlorite, perborate, chlorine dioxide, hydrogen peroxide, etc. and/or a reductive bleach using, for example, sulfur dioxide, metabisulfite, etc. Problems encountered when including a bleaching step prior to preservation and dyeing includes weakened plant material due to attack of the bleach on the plant cellulose, shriveling of leaves and flower petals, etc.
A need exists to improve the known techniques of plant material preservation and/or dyeing.